Subdivided magnetic core with polystyrene binder



April 22, 1941. E. FISCHER 2,238,893

SUBDIVIDED MAGNETIC CORE WITH POLYSTYRENE BINDER Original Filed April17, 1934 Maw.

Patented Apr. 22, 1941 SUBDIVIDED MAGNETIC CORE WITH POLYSTYRENE BINDERErnst Fischer, Berlin-Llchterfelde, Germany, as-

signor to Siemens & Halske Aktiengesellsehaft, Siemensstadt, nearBerlin, Germany, a corporation of Germany Original application April 17,1934, Serial No. 720,923. Divided and this application May 25, 1938,Serial No. 209,917. In Germany April 21, 193

1 Claim.

My invention relates to magnet coils having a magnet core composed ofindividual ferroma netic elements and an insulating binder, such asinductive loading and repeating coils and the like for communicationcables.

This is a division of my application, Serial No. 720,923, filed April1'7, 1934, and is also related to my co-pending application, Serial No.209,918, filed May 25, 1938, also dealing with magnet coils of theabove-mentioned type.

According to the present invention, the magnet cores of magnet coils,such as loading or repeating coils, which are composed of individualelements, such as sheet iron, ribbons, powder particles, and the like,are insulated from and firmly bound together by a solid binding agentconsisting of thermoplastic and non-hygroscopic substance, polystyrenebeing used as such substance. By non-hygroscopic I mean a resistance tohumidity at least as high as that of gutta-percha or other so-callednon-hygroscopic substances customary for submarine cable insulation.

The drawing illustrates for example an enclosed loading coil accordingto my invention.

Fig. 1 shows the coil and its enclosure by a top view partly in section,and

Fig. 2 shows the coil without enclosure in a sectional view taken at aright angle with respect to that of Fig. 1.

With reference to Fig. l, numeral 52 denotes the loading coil enclosedin a metallic covering 33, and M an insulating compound consisting, forinstance, of hydrogenated synthetic rubber.

According to Fig. 2, the coil I2 is composed of an annular magnet core20 and windings 2| surrounding the core. The core consists of individualelements, namely, pressed magnetizable powder particles which areinsulated from one another by polystyrene. The wires of winding 2! mayalso be insulated by polystyrene or another non-hygroscopic substance.

Magnet coils according to the invention have a number of advantages overcoils, the cores of which are composed in the known manner. Polystyrene,being used according to the invention as binding agent of the coreparticles, affords a considerable improvement of the dielectric andmagnetic properties of the core in combination with excellent bindingproperties, and has also an exceptionally low hygroscopicity so that theenhanced dielectric and magnetic properties of the core are furtherdistinguished by an increased stability. The magnet coils thereforemaintain their qualities even if exposed to Water.

The coils or cores, therefore, may be' stored in the factory for aconsiderable time without being deteriorated by humidity, and presentadvantages in all other cases in which an ingress of water to the coilscannot entirely be avoided.

Magnet coils according to the invention present additional advantages inthe form of loading or repeating coils for communication cables,particularly submarine cables. In submarine cables such auxiliaryelements are, as a rule, located in joint boxes with which the cablesare provided in the factory and which are so designed that theflexibility of the submarine cable is only slightly impaired. Particularprecautions must be taken especially in submarine cables in order toprotect the auxiliary elements against the absorption of water, sincesuch absorption would result in a deterioration of the transmittingproperties of the cable and in the expensive replacement of the magnetcoils. However, the penetration of Water into the boxes cannot becompletely avoided. In metallic joint boxes small quantities of watermay penetrate into the box through leaky points of the enclosure, evenif a rubber covering is arranged over the box. Water may also reach thecoils and their magnet body by slowly penetrating through the cableinsulation, and this may occur even in the case of gutta-perchainsulated cables owing to the slight hygroscopicity of gutta-percha. Ithas been found that the compound contained inside the joint boxes is notalone suificient to prevent the further penetration of water, since, asis well known, all compounds are not fully non-hygroscopic and besides,fiaws, cracks and the like are frequently formed in the compound duringthe solidification when pouring the compound into the box and further inthe course of time. If, however, the water has reached the magnet coilsas a result of the flaws, these elements deteriorate in their magneticand electric properties and eventually must be replaced, which causes aninterruption of operation and considerable expense. However, if magnetcoils according to the invention are employed, a magnetic and dielectricdeterioration is prevented.

The polystyrene to be used according to the invention may containadmixtures in particular of non-hygroscopic thermoplastic agents.

According to my invention, polystyrene is em ployed not only forelectrically insulating the ferromagnetic particles of the magnet corefrom one another, but preferably also for insulating the wires formingthe windings of the coil. This use of polystyrene as insulatingsubstance within the magnet core as well as for insulating theindividual wires has especially favorable transmission qualities ofextreme stability against magnetic and dielectric impairments. Thedanger of a deterioration of the magnet coil is further diminished bythe fact that the casing which individually encloses the coil isprovided with a liquid or viscous non-hygroscopic insulating compoundwhich fills all hollow spaces between casing and coil. As fillingcompound, liquid or viscous hydrogenated synthetic rubber isparticularly suitable for this purpose. If desired, other substances maybe added thereto. Other filling compounds may also be employed,particularly such which subsequently become solid or are subsequentlycaused to solidify.

Besides the above-described advantages, a further advantage is attainedin submarine cables according to my invention, in that variousprotective measures which have been hitherto neces= sary may bedispensed with; for instance the arrangement of an additional rubbercovering over the joint box in the case of submarine cables withmetallic sheath. Furthermore, a greater reliability of operation isobtained if the submarine cable is divided into short manufacturinglengths and the auxiliary elements are arranged therein at shortintervals, which is in many cases of advantage from an electrical pointof view. The attainment of the favorable electrical properties ofsubmarine cables brought'about by the loading coils has been hithertofrequently given up owing to the fact that the number of the faultysources is the greater, the shorter the distance at which the auxiliarycoils were arranged. The invention now enables a full utilization of theadvantage of inserting the coils without diminishing the reliability.

I claim:

A non-hygroscopic magnet core for inductance coils for electriccommunication systems subject to high-humidity conditions, consisting ofa pressed solid mixture of ferromagnetic powder and an insulating binderconsisting of polystyrene and being non-hygroscopic to a degreecustomary in submarine cable insulation.

ERNST FISCHER.

